MySQL> use test; create table test(a varchar(512) primary key, b varchar(1024));
Database changed
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
drop table if exists test;
create table test(test varchar(767) primary key)charset=latin5;
-- 成功
drop table if exists test;
create table test(test varchar(768) primary key)charset=latin5;
-- 错误
-- ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
drop table if exists test;
create table test(test varchar(383) primary key)charset=GBK;
-- 成功
drop table if exists test;
create table test(test varchar(384) primary key)charset=GBK;
-- 错误
-- ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
drop table if exists test;
create table test(test varchar(255) primary key)charset=UTF8;
-- 成功
drop table if exists test;
create table test(test varchar(256) primary key)charset=UTF8;
-- 错误
-- ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
原因：
MySQL的varchar主键只支持不超过768个字节,或者768/2=384个双字节,或者768/3=256个三字节的字段,而GBK是双字节的，UTF-8是三字节的。
变量设置：
mysql> show variables like '%char%';
+--------------------------+--------------------------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | latin1 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /opt/schooner/ac_3.1/mysql/share/mysql/charsets/ |
+--------------------------+--------------------------------------------------+
8 rows in set (0.00 sec)